Active-matrix liquid crystal display having storage capacitors of area smaller than that of pixel electrodes

ABSTRACT

An active-matrix liquid crystal display has storage capacitors each having a small area relative to the area of each of pixel electrodes and has a large aperture ratio. A plurality of gate lines are formed on a lower substrate and a plurality of source lines are formed on the lower substrate so as to extend perpendicularly to the gate lines. Thin-film transistors are formed near the intersections of the gate lines and the source lines. Pixel electrodes are connected to the thin-film transistors and storage capacitors. Each storage capacitor includes an upper electrode, a lower electrode disposed opposite to the upper electrode, and an insulating film sandwiched between the upper and the lower electrode. The insulating film for the storage capacitors and gate insulating film for the thin-film transistors are formed separately. The insulating film for the storage capacitors is formed of a material different from that of the gate insulating film in a thickness smaller than that of the gate insulating film so that the storage capacitors have a large capacitance per unit area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active-matrix liquid crystal displayhaving a display screen provided with a plurality of pixel electrodes,thin-film transistors (hereinafter referred to as “TFTs”) as switchingelements respectively corresponding to the pixel electrodes, and storagecapacitors respectively corresponding to the pixel electrodes.

2. Description of the Related Art

The configuration of a conventional active-matrix liquid crystal displaywill be described with reference to FIGS. 7 and 8. FIG. 8 is a plan viewof an essential part of an array substrate underlying a liquid crystalincluded in the active-matrix liquid crystal display, and FIG. 7 is asectional view taken on line 7—7 in FIG. 8 and showing the essentialpart of the array substrate, a liquid crystal layer and an arrangementoverlying the liquid crystal layer. As shown in FIG. 7, a liquid crystallayer 31 is filled and sealed in a space between a transparent lowersubstrate 32 and a transparent upper substrate 33 disposed opposite tothe lower substrate 32. Polarizing plates 34 and 35 are attached to therespective outer surfaces of the lower substrate 32 and the uppersubstrate 33, respectively. Transparent pixel electrodes 36 are formedon the inner surface of the lower substrate 32, and common electrodes 37are formed on the inner surface of the upper substrate 33 opposite tothe pixel electrodes 36.

Referring to FIG. 8, formed on the lower substrate 32 are a plurality ofparallel gatelines 42, i.e., scanning lines, and a plurality of parallelsource lines 40, i.e., signal lines, extending perpendicularly to thegate lines 42.

The transparent pixel electrodes 36 are formed in rectangular regionssurrounded by the gate lines 42 and the source lines 40, respectively. ATFT 38, i.e., a switching element, formed near the intersection of eachsource line 40 and each gate line 42. The TFT 38 turns on to apply adata signal voltage to the corresponding pixel electrode 36 and turnsoff to shut the data signal voltage to the same pixel electrode 36.Thin-film storage capacitors Cs for holding charges on the pixelelectrodes 36 are formed on the gate lines 42.

Each of the TFTs 38 includes a source electrode 40 a extending from thesource line 40, a drain electrode 41, a gate electrode 42 a extendingfrom the gate line 42 and a gate insulating film 43. The drain electrode41 is connected through a contact hole 45 formed in a layer insulatingfilm 44 to the pixel electrode 36. The pixel electrode 36 is connectedthrough a contact hole 46 to the upper electrode 47 of the storagecapacitor Cs. The gate line 42 formed on the lower substrate 32 servesas the lower electrode of the storage capacitor Cs. The upper electrode47 is disposed opposite to the gate line 42 with the gate insulatingfilm 43 interposed therebetween.

In this conventional active-matrix liquid crystal display, a data signalvoltage is applied to a selected one of the plurality of source lines 40and a control signal is applied to a selected one of the plurality ofgate lines 42 to drive the TFT 38 connected to the selected source line40 and the selected gate line 42, whereby the data signal voltage isapplied to the pixel electrode 36 connected to the drain electrode 41 ofthe TFT 38. The TFTs 38 respectively connected to the pixel electrodes36 arranged in a matrix are thus driven to display a desired pattern onthe screen.

As shown in FIG. 7, the gate insulating film 43 of the TFT 38 servesalso as an insulating film for the storage capacitor Cs. Use of a singlefilm formed by a single process as both the gate insulating film 43 andthe insulating film for the storage capacitor Cs is favorable in view ofsimplifying a liquid crystal display fabricating process. The thicknessof the film is determined so that the gate insulating film 43 of the TFT38 has a sufficient dielectric strength.

Although dependent on the configuration of the storage capacitor Cs, avoltage to be applied to the storage capacitor Cs is in the range of ¼to ½ of a voltage to be applied to the TFT 38. Therefore, a thickness ofthe insulating film for the storage capacitor Cs having a sufficientdielectric strength may be smaller than that of the gate insulating film43 of the TFT 38. Thus, the thickness of the gate insulating film 43 ofthe TFT 38 is excessively great for the insulating film for the storagecapacitor Cs.

The area of the storage capacitor Cs is calculated by dividing apredetermined charge storage capacity necessary for driving the pixelelectrode 36 by the storage capacity per unit area of the thin-filmstorage capacitor Cs. Since the storage capacity per unit area isuniquely dependent on the dielectric constant and the thickness of thegate insulating film 43, the area of the storage capacitor Cs isdetermined on the basis of the dielectric constant and the thickness ofthe gate insulting film 43.

An active-matrix liquid crystal display must have a high opticaltransmittance, i.e., a large aperture ratio, to display pictures in ahigh picture quality. When the size of pixels is reduced forhigh-definition displaying, an area occupied by the storage capacitorsCs increases relatively and hence the aperture ratio is reduced. If thebrightness of back light is increased to compensate the reduction of theaperture ratio, the power consumption of the active-matrix liquidcrystal display increases.

The area of the storage capacitors Cs needs to be reduced to increasethe aperture ratio. However, since the insulating film for the storagecapacitors Cs is part of the gate insulating film 43 of the TFTs 38 andthe thickness of the gate insulating film 43 is determined on the basisof the dielectric strength of the TFTs 38, the capacitance per unit areaof the storage capacitor Cs cannot be individually increased.Consequently, the area of the storage capacitor Cs cannot be reducedsecuring the predetermined capacitance of the storage capacitor Cs andthe aperture ratio decreases inevitably when the size of the pixels isreduced for high-definition displaying.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anactive-matrix liquid crystal display having a large aperture ratioachieved by forming storage capacitors each having a small area relativeto that of pixel electrodes.

According to a first aspect of the present invention, an active-matrixliquid crystal display comprises: a transparent upper substrate; atransparent lower substrate disposed opposite to the upper substrate; aliquid crystal filled and sealed in a space between the upper and thelower substrate; a plurality of parallel gate lines formed on the lowersubstrate; a plurality of parallel source lines formed on the lowersubstrate so as to extend perpendicularly to the gate lines; TFTs formedat intersections of the gate lines and the source lines, respectively;pixel electrodes connected to the TFTs, respectively; and storagecapacitors connected to the pixel electrodes, respectively; whereinseparate films are used as an insulating film included in the storagecapacitors and a gate insulating film included in the TFTs,respectively, and each of the storage capacitors has an upper electrodeconnected to the pixel electrode and a lower electrode disposed oppositeto the upper electrode with the insulating film sandwiched between theupper and the lower electrode. The capacitance per unit area of thestorage capacitors can be determined independently of the thickness ofthe gate insulating film for the TFTs. Therefore, the area of eachstorage capacitor can be reduced relative to the area of each pixelelectrode by increasing the capacitance per unit area of the storagecapacitors.

Preferably, the upper electrodes are formed only in flat regions on theinsulating film overlying the lower electrodes. When the upperelectrodes are thus, formed, dielectric breakdown at steps in theinsulating film around the lower electrode does not occur easily.Therefore, the thickness of the insulating film can be reduced so as tomeet the required dielectric strength of the storage capacitors, whichenables the further increase of the capacitance per unit area of thestorage capacitors.

Preferably, the insulating film for the storage capacitors and the gateinsulating film for the TFTs are formed of the same material, and thethickness of the insulating film for the storage capacitors is smallerthan that of the gate insulating film for the TFTs. A gate insulatingfilm forming process can be applied to forming the insulating film.Thus, the capacitance per unit area of the storage capacitors can beincreased and the area of each storage capacitor can be reduced relativeto the area of each pixel electrode without complicating anactive-matrix liquid crystal display fabricating process.

The insulating film for the storage capacitors may be formed of amaterial having a dielectric constant greater than that of a materialforming the gate insulating film. Thus, the capacitance per unit of thestorage capacitors can be increased and the area of each storagecapacitor can be reduced relative to that of the pixel electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary sectional view of an active-matrix liquidcrystal display in a first embodiment according to the presentinvention;

FIG. 2 is a plan view of an essential part of an array substrateincluded in the active-matrix liquid crystal display shown in FIG. 1;

FIG. 3 is a fragmentary sectional view of an active-matrix liquidcrystal display in a second embodiment according to the presentinvention;

FIG. 4 is a plan view of an essential part of an array substrateincluded in the active-matrix liquid crystal display shown in FIG. 3;

FIG. 5 is a fragmentary sectional view of an active-matrix liquidcrystal display in a third embodiment according to the presentinvention;

FIG. 6 is a plan view of an essential part of an array substrateincluded in the active-matrix liquid crystal display shown in FIG. 5;

FIG. 7 is a fragmentary sectional view of a conventional active-matrixliquid crystal display; and

FIG. 8 is a plan view of an essential part of an array substrateincluded in the active-matrix liquid crystal display shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An active-matrix liquid crystal display in a first embodiment accordingto the present invention will be described with reference to FIGS. 1 and2. FIG. 2 is a plan view of an essential part of an array substrateincluded in the active-matrix liquid crystal display and FIG. 1 is asectional view taken on line 1—1 in FIG. 2, showing the array substratecombined with a liquid crystal layer and upper components. Referring toFIGS. 1 and 2, the active-matrix liquid crystal display has atransparent lower substrate 1 of glass, a transparent upper substrate 2of glass disposed opposite to the lower substrate 1 so as to define aspace between the substrates 1 and 2, and a liquid crystal layer 3filled and sealed in the space between the substrates 1 and 2. Gatelines 7 and 7′ and gate electrodes 7 a are formed on the lower substrate1. A gate insulating film 8 of a thickness in the range of 3000 to 5000Å is formed so as to cover the gate lines 7 and 7′ and the gateelectrodes 7 a.

The gate insulating film 8 is formed of silicon nitride (SiN_(x)) or thelike. Openings 9 are formed in part of the gate insulating film 8overlying the gate lines 7′ in regions corresponding to storagecapacitors Cs to form the storage capacitors Cs therein. An insulatingfilm 10 for forming the storage capacitors Cs is formed on the gateinsulating film 8. In the following description, an insulating film forthe storage capacitors Cs will be referred to simply as “insulatingfilm”, and other insulating films will be referred to as “gateinsulating film” and “interlayer insulating film” signifying thefunctions of the insulating films. The insulating film 10 is formed of amaterial having a large dielectric constant, for example, SiN_(x),tantalum oxide (TaOx) such as Ta₂O₅. The insulating film 10 has athickness smaller than that of the gate insulating film 8. In the firstembodiment, both the gate insulating film 8 and the insulating film 10are formed of SiN_(x). The insulating film 10 is formed in a thicknessgreat enough to secure a dielectric strength necessary for the storagecapacitors Cs. The thickness of the insulating film 10 is in the rangeof 500 to 1500 Å.

TFTs 11 are formed on the insulating film 10 in regions above the gateelectrodes 7 a. Each TFT 11 has a source electrode 13 a extending fromthe source line 13, and a drain electrode 14. The source electrode 13 aand the drain electrode 14 are formed on the opposite side parts ofchannel forming region of a semiconductor layer 12 of amorphous silicon(a-Si) The superposed gate insulating film 8 and the insulating film 10serves as the gate insulating film for the TFT 11. Each storagecapacitor Cs has a lower electrode and an upper electrode 15. The gateline 7′ serves as the lower electrode of each storage capacitor Cs. Theinsulating film 10 is sandwiched between the gate line 7′, i.e., thelower electrode, and the upper electrode 15. The upper electrode 15 isformed only in a flat region of the insulating film 10 and hencedielectric breakdown at steps in the insulating film 10 does not occureasily. Therefore, the insulating film 10 may be thin and hence thestorage capacitor Cs has a large capacitance per unit area.

The source lines 13, the source electrodes 13 a, the drain electrodes 14and the upper electrodes 15 may be formed of the same metal, such aschromium (Cr), molybdenum (Mo), aluminum (Al) or the like in a thicknessin the range of 1000 to 3000 Å. Although the gate lines 7′ are used asthe lower electrodes of the storage capacitors Cs in the firstembodiment, special wiring lines maybe used instead of the gate lines 7′for forming the lower electrodes.

The interlayer insulating film 16 is formed of a polymer, such as aphotosensitive polyimide, in a thickness in the range of 1 to 3 μm.Contact holes 17, 18 respectively reaching the drain electrodes 14 andthe upper electrodes 15 are formed in the interlayer insulating film 16.A film of indium tin oxide (ITO) or the like of a thickness in the rangeof 500 to 1500 Å is formed on the interlayer insulating film 16 and isprocessed to form pixel electrodes 19. The pixel electrodes 19 areconnected through the contact holes 17 and 18 to the drain electrodes 14and the upper electrodes 15, respectively. A common electrode 4 of ITOor the like is formed on a surface of the upper substrate 2 facing thelower substrate 1. Polarizing plates 5 and 6 are attached to the outersurfaces of the substrates 1 and 2, respectively.

As shown in FIG. 2, the TFTs 11 are formed near the intersections of thesource lines 13 and the gate lines 7 and 7′ extended perpendicularly tothe source lines 13. Each storage capacitor Cs is formed by laminatingthe upper electrode 15 connected to the pixel electrode 19, theinsulating film 10, and the gate line 7′ connected to the TFT foranother pixel electrode in that order. The gate line 7′ serves as thelower electrode of the storage capacitor Cs.

The transparent lower substrate 1 provided with the storage capacitorsCs is formed by the following process. A metal film of Cr, Mo, Al or thelike for forming the plurality of gate lines 7 and 7′ and the gateelectrodes 7 a extending from the gate lines 7 and 7′ is formed on thetransparent lower substrate 1, and the metal film is etched forpatterning. The gate insulating film 8 for the TFTs 11 is formed. Partsof the gate insulating film 8 over the parts of the gate lines 7′serving as the lower electrodes of the storage capacitors Cs are removedby etching to form the openings 9 for the storage capacitors Cs.Generally, the gate insulating film 8 is formed by a CVD process whenSiNx is used for forming the gate insulating film 8.

Then, the insulating film 10 is formed. The insulating film 10 is formedon the gate insulating film 8 in regions corresponding to the TFTs 11and serves as part of a film for forming gates. Then, the semiconductorlayer 12 for forming the channels of the TFTs 11 is formed. A metal filmfor forming the source lines 13, the source electrodes 13 a extendingfrom the source lines 13, the drain electrodes 14 and the upperelectrodes 15 of the storage capacitors Cs is formed by a sputteringprocess. The semiconductor layer 12 is patterned to complete the TFTs 11and the storage capacitors Cs. The upper electrodes 15 are formed onlyin flat regions of the insulating film 10.

Subsequently, the interlayer insulating film 16 of a photosensitiveorganic material is formed by a spin coating process, and the contactholes 17 and 18 are formed in the interlayer insulating film 16 by aphotolithographic process. A transparent conductive film for forming thepixel electrodes 19 is formed by a sputtering process, and thetransparent conductive film is patterned by etching to form the pixelelectrodes 19. The pixel electrodes 19 are connected through the contactholes 17 to the drain electrodes 14, respectively, and through thecontact holes 18 to the upper electrodes 15 of the storage capacitorsCs, respectively.

The transparent lower substrate 1 thus fabricated and the transparentupper substrate 2 provided with the common electrode 4 are combined soas to form a space between the substrates 1 and 2, a liquid crystal isfilled and sealed in the space between the substrates 1 and 2, and thepolarizing plates 5 and 6 are attached to the outer surfaces of thesubstrates land 2, respectively, to complete the active-matrix liquidcrystal display in the first embodiment.

The thickness of the insulating film 10 for the storage capacitors Cs ofthe first embodiment is about ⅓ or below of that of the correspondingfilm of the conventional active-matrix liquid crystal display and thestorage capacitors Cs have a large capacitance per unit area.Accordingly, the area of each storage capacitor Cs is smaller than thatof the pixel electrode 19. Consequently, the active-matrix liquidcrystal display in the first embodiment has an aperture ratio of 55%,whereas the conventional active-matrix liquid crystal display has anaperture ratio of about 40% at the greatest.

An active-matrix liquid crystal display in a second embodiment accordingto the present invention will be described with reference to FIGS. 3 and4, in which parts like or corresponding to those shown in FIGS. 1 and 2are denoted by the same reference characters and the description thereofwill be omitted. FIG. 4 is a plan view of an essential part of an arraysubstrate included in the active-matrix liquid crystal display and FIG.3 is a sectional view taken on line 3—3 in FIG. 4, showing the arraysubstrate combined with a liquid crystal layer and upper components.Part of a process for fabricating the active-matrix liquid crystaldisplay in the second embodiment from the first step to steps of formingthe gate insulating film 8 for the TFTs 11 and removing parts of thegate insulating film 8 overlying the gate lines 7′ is the same as thatof the process for fabricating the active-matrix liquid crystal displayin the first embodiment. After forming the semiconductor layer 12 forforming the channels of the TFTs 11, a metal film for forming the sourcelines 13, the source electrodes 13 a extending from the source lines 13,the drain electrodes 14 and an auxiliary electrodes 20 forming part ofthe lower electrodes of the storage capacitors Cs is formed. The metalfilm is patterned by etching. Parts of the insulating film 8 overlyingthe gate lines 7′ are removed to form the openings 9 for the storagecapacitors Cs so as to expose parts of the gate lines 7′, and theauxiliary electrodes 20 are formed on the exposed parts of the gatelines 7′. The auxiliary electrodes 20 forms the lower electrodes of thestorage capacitors Cs together with the gate lines 7′.

The insulating film 10 for the storage capacitors Cs is formed over theentire surface of the lower substrate 1 including regions in which theTFTs 11 are formed. Parts of the insulating film 10 corresponding tocontact holes 21 to be connected to the drain electrodes 14 are removedby etching. Then, the interlayer insulating film 16 is formed over theentire surface of the lower substrate 1, and parts of the interlayerinsulating film 16 corresponding to the contact holes 17 to be connectedto the drain electrodes 14 and parts of the same corresponding toregions where the storage capacitors Cs are to be formed, i.e., partscorresponding to flat parts of the insulating film 10 overlying theauxiliary electrodes 20, are removed by a photolithographic process. Inthis step, the interlayer insulating film 16 may be formed immediatelyafter forming the insulating film 10, and the contact holes 17 in theinterlayer insulating film 16 and the contact holes 21 in the insulatingfilm 10 may be formed successively by etching.

In the second embodiment, the upper electrodes 15 of the storagecapacitors Cs is formed of the transparent conductive film forming thepixel electrodes 19. Therefore, parts of the interlayer insulating film16 must be removed so that the pixel electrodes 19 are formed over theentire regions of the storage capacitors Cs and the upper electrodes 15are formed in flat parts of the insulating film 10. After thus removingparts of the interlayer insulating film 16, a transparent conductivefilm is formed, and the pixel electrodes 19 and the upper electrodes 15of the storage capacitors Cs are formed simultaneously by patterning.

Basically, the effect of the second embodiment is the same as that ofthe first embodiment. The second embodiment differs from the firstembodiment in not using the insulating film 10 for the storagecapacitors Cs as the gate insulating film that affects the operation ofthe TFTs 11. Therefore, the material forming the insulating film 10 forthe storage capacitors Cs can be optionally determined without affectingthe performance of the TFTs 11. For example, TaO_(x) or the like havinga dielectric constant greater than that of SiN_(x), can be relativelyeasily used to increase the capacitance per unit area of the storagecapacitors Cs. Since the auxiliary electrodes 20 overlie considerablylarge parts of the gate lines 7 and 7′, the total wiring resistance ofthe gate lines 7 and 7′ is reduced by the secondary effect of the secondembodiment.

In the second embodiment, the insulating film 10 for the storagecapacitors Cs may be formed of SiN_(x) as well as the gate insulatingfilm 8. Preferably, the thickness of the insulting film 10 is equal tothat of the insulating film 10 of the first embodiment. The other filmsof the second embodiment may be the same in material and thickness asthe corresponding films of the first embodiment.

An active-matrix liquid crystal display in a third embodiment accordingto the present invention will be described with reference to FIGS. 5 and6, in which parts like or corresponding to those shown in FIGS. 3 and 4are denoted by the same reference characters and the description thereofwill be omitted. FIG. 6 is a plan view of an essential part of an arraysubstrate included in the active-matrix liquid crystal display and FIG.5 is a sectional view taken on line 5—5 in FIG. 6, showing the arraysubstrate combined with a liquid crystal layer and upper components. Thethird embodiment is based on the same conception as that on which thesecond embodiment is based. In the third embodiment, the insulating film10 for the storage capacitors Cs is not used for forming the gateinsulating film for the TFTs 11. Part of a process for fabricating theactive-matrix liquid crystal display in the third embodiment from thefirst step to a step of forming the semiconductor layer 12 is the sameas that of the process for fabricating the active-matrix liquid crystaldisplay in the second embodiment.

The insulating film 10 for the storage capacitors Cs is formed over theentire surface of the lower substrate 1, and parts of the insulatingfilm 10 corresponding channels electrically connected to the sourceelectrodes 13 a and the drain electrodes 14 overlying the semiconductorlayer 12 and parts for forming channels are removed by etching to formcontact holes 22. A metal film for forming the source lines 13, thesource electrodes 13 a extending from the source lines 13, the drainelectrodes 14 and the upper electrodes 15 of the storage capacitors Csis formed over the entire surface of the lower substrate 1, and themetal film is patterned by etching. The upper electrodes 15 are formedonly in flat regions of the insulating film 10 overlying the gate lines7′ serving as the lower electrodes. A process for forming the interlayerinsulating film 16, the photolithographic process, a process for formingthe transparent conductive film and a process for patterning thetransparent conductive film to form the pixel electrodes 19 are the sameas those employed in fabricating the first embodiment.

The third embodiment, similarly to the second embodiment, increases thedegree of freedom of selecting a material for forming the insulatingfilm 10 for the storage capacitors Cs, and the thickness of a filmbetween the source electrode 13 a and the gate electrode 7 a and thethickness of a film between the drain electrode 14 and the gateelectrode 7 a are increased by the thickness of the insulating film 10.Consequently, the transistors TFTs 11 have a high dielectric strength.The aperture ratios of the second and the third embodiment, similarly tothat of the first embodiment, are as large as about 55%.

As apparent from the foregoing description, the storage capacitor Csincludes the upper electrode connected to the pixel electrode, the lowerelectrode disposed opposite to the upper electrode and the insulatingfilm sandwiched between the upper and the lower electrode, and theinsulating film is different from the gate insulating film for the TFT.Therefore, the insulating film for the storage capacitors Cs can beformed in a small thickness independently of the thickness of the gateinsulating film and/or the insulating film can be formed of a materialhaving a large dielectric constant. Thus, the capacitance per unit areaof the storage capacitors Cs can be increased. Consequently, the area ofthe storage capacitors Cs necessary for securing a predeterminedcapacitance may be small as compared with that of the pixel electrodesand the active-matrix liquid crystal display even for high-definitiondisplaying has a large aperture ratio.

Although the invention has been described in its preferred embodimentswith a certain degree of particularity, obviously many changes andvariations are possible therein. It is therefore to be understood thatthe present invention may be practiced otherwise than as specificallydescribed herein without departing from the scope and spirit thereof.

What is claimed is:
 1. An active-matrix liquid crystal displaycomprising: a transparent upper substrate; a transparent lower substratedisposed opposite to the upper substrate; a liquid crystal filled andsealed in a space between the upper and the lower substrate; a pluralityof parallel gate lines formed on the lower substrate; a plurality ofparallel source lines formed on the lower substrate so as to extendperpendicularly to the gate lines; thin-film transistors formed atintersections of the gate lines and the source lines, respectively;pixel electrodes connected to the thin-film transistors, respectively;and storage capacitors connected to the pixel electrodes, respectively;wherein separate films are used as an insulating film included in thestorage capacitors and a gate insulating film included in the thin-filmtransistors, respectively, and each of the storage capacitors has anupper electrode connected to the pixel electrode and a lower electrodedisposed opposite to the upper electrode with the insulating filmsandwiched between the upper and the lower electrode.
 2. Theactive-matrix liquid crystal display according to claim 1, wherein theupper electrodes are formed only in flat regions, respectively, on theinsulating film overlying the lower electrodes.
 3. The active-matrixliquid crystal display according to claim 1, wherein the insulating filmfor the storage capacitors and the gate insulating film for the TFTs areformed of the same material, and a thickness of the insulating film forthe storage capacitors is smaller than that of the gate insulating filmfor the TFTs.
 4. The active-matrix liquid crystal display according toclaim 1, wherein the insulating film for the storage capacitors isformed of a material having a dielectric constant greater than that of amaterial forming the gate insulating film.
 5. The active-matrix liquidcrystal display according to claim 1, wherein the gate insulating filmhas an opening above and smaller than the lower electrode, the openingof the gate insulating film has edges, and the insulating film iscontinuously disposed above the gate insulating film and the opening ofthe gate insulating film from a portion of the gate insulating filmproximate to and on one side of the lower electrode to a portion of thegate insulating film proximate to and on an opposing side of the lowerelectrode.
 6. The active-matrix liquid crystal display according toclaim 5, wherein the upper electrode has a smaller width than the lowerelectrode.
 7. The active-matrix liquid crystal display according toclaim 6, wherein the upper electrode is formed in the opening of thegate insulating film.
 8. The active-matrix liquid crystal displayaccording to claim 7, wherein the upper electrode and lower electrodeare separated substantially entirely by the insulating film.
 9. Theactive-matrix liquid crystal display according to claim 8, wherein thesource electrodes are disposed above the insulating film and contactsides of semiconductor layers of the thin-film transistors.
 10. Theactive-matrix liquid crystal display according to claim 8, wherein thesource electrodes are disposed above the insulating film and contactsemiconductor layers of the thin-film transistors only on a top of thesemiconductor layers.
 11. The active-matrix liquid crystal displayaccording to claim 1, wherein the source electrodes are disposed abovethe insulating film and contact sides of semiconductor layers of thethin-film transistors.
 12. The active-matrix liquid crystal displayaccording to claim 1, wherein the source electrodes are disposed abovethe insulating film and contact semiconductor layers of the thin-filmtransistors only on a top of the semiconductor layers.
 13. Theactive-matrix liquid crystal display according to claim 1, wherein athickness of the gate insulating film is at least three times athickness of the insulating film.
 14. The active-matrix liquid crystaldisplay according to claim 1 wherein an aperture ratio of theactive-matrix liquid crystal display is at least about 55%.
 15. Anactive-matrix liquid crystal display comprising: a transparent uppersubstrate; a transparent lower substrate disposed opposite to the uppersubstrate; a liquid crystal filled and sealed in a space between theupper and the lower substrate; a plurality of parallel gate lines formedon the lower substrate; a plurality of parallel source lines formed onthe lower substrate so as to extend perpendicularly to the gate lines;thin-film transistors formed at intersections of the gate lines and thesource lines, respectively, and having a gate insulating film; pixelelectrodes connected to the thin-film transistors, respectively; lowerelectrodes disposed below the pixel electrode; auxiliary electrodesdisposed between the lower electrodes and the pixel electrodes; and aseparate insulating film disposed between the auxiliary electrodes andthe pixel electrodes; the insulating film, pixel electrodes, auxiliaryelectrodes, and lower electrodes forming a storage capacitor.
 16. Theactive-matrix liquid crystal display according to claim 15, wherein theinsulating film for the storage capacitors and the gate insulating filmfor the TFTs are formed of the same material, and the thickness of theinsulating film for the storage capacitors is smaller than that of thegate insulating film for the TFTs.
 17. The active-matrix liquid crystaldisplay according to claim 15, wherein the insulating film for thestorage capacitors is formed of a material having a dielectric constantgreater than that of a material forming the gate insulating film. 18.The active-matrix liquid crystal display according to claim 17, whereinthe auxiliary electrode is formed in the opening of the gate insulatingfilm.
 19. The active-matrix liquid crystal display according to claim15, wherein the gate insulating film has an opening above and smallerthan the lower electrode, the opening of the gate insulating film hasedges, and the insulating film is continuously disposed above the gateinsulating film and the opening of the gate insulating film from aportion of the gate insulating film proximate to and on one side of thelower electrode to a portion of the gate insulating film proximate toand on an opposing side of the lower electrode.
 20. The active-matrixliquid crystal display according to claim 15, wherein the lowerelectrode and auxiliary electrode have the same width.
 21. Theactive-matrix liquid crystal display according to claim 15, wherein theinsulating film is disposed above the source electrodes.
 22. Theactive-matrix liquid crystal display according to claim 15, wherein athickness of the gate insulating film is at least three times athickness of the insulating film.